Checking if container is sorted

[jchutrue]

The numpy diff() function returns an array of the same type as its input. This means that we have to be careful about checking whether a generic container is sorted if that container is of an unsigned type. Currently various jagular functions rely on diff(), including get_contiguous_segments() and may have to be modified if necessary.

[eackermann]

Both is_sorted and is_sorted_np do not rely on np.diff and we should be good to go. There are some other instances of np.diff still scattered around; some are potentially problematic, and some certainly are not, so I'm leaving this open until we have time to do a comprehensive clean-up and vetting.